This is part of the poem, Bed in Summer by Robert Louis Stevenson. I chose to publish only the first stanza, because it is better fitting to this time of year as the days get shorter. This poem leaped into my head this morning as I awoke for the day in the pitch dark.
"Slavery ended in medieval Europe only because the church extended its sacraments to all slaves and then managed to impose a ban on the enslavement of Christians (and of Jews). Within the context of medieval Europe, that prohibition was effectively a rule of universal abolition. "— Rodney Stark